She was sacked from her £126,000-a-year post in the firm’s Moscow office in February last year for “gross misconduct” after her website, chronicling the sexual adventures of an apparently fictional high-flying young businesswoman, allegedly brought the firm into disrepute.

Now the 44 year-old American, who has since become a “sexpat” columnist for the English-language Moscow News newspaper, is suing the firm for £3.49 million in damages claiming sexual discrimination and unfair dismissal.

Allen & Overy, which is part of the "magic circle'' of major City law firms and employs 5,500 people around the world, denied the claim, saying it would “vigorously defend” the allegations.

In papers tendered to Stratford Employment Tribunal, in east London, Miss Clark claims her boss, Tony Humphrey, 60, became “sexually obsessed” after they were intimate at a staff party.

Miss Clark claimed the novel had nothing to do with her colleagues but conceded it was partly autobiographical.

She insisted, however, that she should have been free to publish what was ultimately a work of fiction, saying her case was about defending freedom of expression

Mr Humphrey, who is the firm’s Global Head of Russia Practice Group and Managing Partner, declined to comment.

A spokesman for the firm said: “We are aware of (Miss Clark's) employment tribunal claim.

“We are entirely satisfied that the termination of her employment was justified and lawful and will defend Ms Dare's claim vigorously."

He declined to answer further specific questions, as it was “before the tribunal”.

Miss Clark’s newspaper columns have sometimes stirred controversy. In particular, an article last November called “Come on, cavemen!” drew a furious response from some readers who accused her of condoning rape.

“Men are born to fight and rape,” she wrote in The Moscow News.

“It’s hard to call something ‘wrong’ if it’s simply part of human nature. When it goes to raping and pillaging, I say: Bring it on, baby!.”

Miss Dare later apologised for any offence, denying she condoned rape or violence against women.

"I will also note that I see a therapist weekly,” she added.

The parties are due at the tribunal on Tuesday for a private preliminary hearing.